Caption: Scanning electron micrograph (SEM) of Vibrio fischeri, Gram-negative, motile, bioluminescent, curved rod-shaped bacterium (prokaryote). Vibrio fischeri occurs in global ocean environments. V. fischeri is most often found in a symbiotic relationship with certain deep sea marine life, such as the bobtail squid, within special light-organs. V. fischeri causes the squid to produce a mucus substance that is secreted below the light organ on the squid. Cilia are used to draw more bacteria into this mucus matrix. The bacteria migrate into the light organ and colonize an area within it. They provide a light source for the squid to make it blend in with the ocean floor at night. Thus predators have a hard time seeing the squid. V. fischeri is a key research organism for examination of microbial bioluminescence, quorum sensing, and bacterial-animal symbiosis. Magnification: x8,000 when shortest axis printed at 25 millimetres.